Substrate binding domain of ABC-type phosphonate uptake system; contains the type 2 periplasmic binding fold
This subfamily includes the Escherichia coli PhnD (EcPhnD) which exhibits high affinity for the environmentally abundant 2-aminoethylphosphonate (2-AEP), a precursor in the biosynthesis of phosphonolipids, phosphonoproteins, and phosphonoglycans. The Escherichia coli phn operon encodes 14 genes involved in binding, uptake and metabolism of phosphonate, and is activated under phophophate-limiting conditions. PhnD belongs to the PBP2 superfamily of periplasmic binding proteins that differ in size and ligand specificity, but have similar tertiary structures consisting of two globular subdomains connected by a flexible hinge. The PBP2 have been shown to bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. PhnD is the periplasmic binding component of an ABC-type phosphonate uptake system (PhnCDE) that recognizes and binds phosphonate.
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